The biology of the midseason pitching slump

William Blewett

The All-Star Game brings more than just a midseason shot of excitement to Major League Baseball. It provides much-needed rest for the players, a four-day respite in a 162-game season that often produces fatigue and injury.

The players who most need rest are the starting pitchers, who, paradoxically, get the most rest during the season, playing only every fifth day. Yet, midseason pitching swoons, like the Oriole starters have recently experienced, are not uncommon.

Perhaps the best-known case of pitching fatigue to occur around the All-Star break was that of Bob Feller, the Cleveland fireballer who at age 17 struck out 17 batters in his fifth major-league start. In his third season, 1938, Mr. Feller fell into a slump after being selected as an all-star. He won nine games before the break, then lost nine games after it. His earned-run average for August soared to 8.71, up from 1.43 in May. Cleveland newspapers declared his fastball gone. No one knew why.

Modern science offers an explanation of Mr. Feller's power outage. The likely cause was fatigue of the most heavily worked muscles of pitching: the wrist flexors and finger flexors of the forearm.

A major-league fastball requires exceptional hand speed and arm speed, which demand an abundance of the powerful fast-glycolytic muscle fibers in the arm and shoulder — the same fiber type Olympic sprinters and jumpers rely on for explosive power. Physiologists have a second name for this high-performance fiber: fast-fatigable.

This fiber fatigues rapidly because its main energy source is a limited supply of microscopic glycogen granules stored in each fiber. A pitcher can deplete the glycogen from his forearm flexors in a single outing, but it takes more than a day to restore the glycogen. If there is substantial micro-trauma to the muscle fibers — a routine occurrence in pitchers' forearm muscles — restoration can take a week or more. The glycogen energy system, technically known as intramuscular storage of energy substrate, is much like a rechargeable battery.

Depletion of glycogen causes muscle fibers to lose power, to contract more slowly under a load. At very low glycogen levels, fibers can shut down — enter a state of stiffness — or begin to act like slow-twitch fibers, relying not on glycogen but on a very small, less-powerful aerobic capacity.

This leads to differential fatigue, in which the flexion of the wrist and fingers lags the arm in its high-speed rotation. The result: the pitcher loses his precise coordination between the two fastest movements of pitching: forward arm rotation, with speeds as high as 10,000 degrees per second, and wrist flexion, up to 4,500 degrees per second.

This temporary loss of perfect coordination affects control, often leaving the fastball up in the strike zone. It also produces a slower spin rate, resulting in less movement of the fastball, making the pitch more easily hittable.

The remedy is simple. Rest. Skip a start. Add an extra rest day to the cycle. Or send the pitcher to the bullpen, where the workload is lighter. Pitchers, however, sometimes work harder in response, worsening the problem.

Because the restoration can take days, the workouts between outings that forcefully activate the fast-glycolytic fibers of the pitching muscles — such as wrist curls, chin-ups, long tossing, or near-game-speed bullpen throwing sessions — delay the full recharging of glycogen.

The effect of muscle micro-trauma on restoration can be seen in the contrast between a no-hitter and the game after the no-hitter, particularly with high pitch counts. Johan Santana threw a no-hitter on June 1, the first in New York Mets history. Seven days later, he gave up six earned runs and four homers in five innings. His manager was blamed for the dismal performance because he delayed the next start by two days. It would likely have been even worse, however, had Mr. Santana stuck to the five-day cycle.

Compared to pitchers of a century ago, pitchers today routinely throw faster, expending more stored energy per pitch. They also train harder during the season, depleting more glycogen between starts. Bad games, short outings, shellings, and inconsistent pitching were less common 100 years ago. There was no All-Star Game then — and no need for a midseason break to forestall pitching fatigue.

William Blewett, who writes from Bel Air, is the author of "The Science of the Fastball" (McFarland & Co.), to be released this fall. His email is wkblewett@aol.com.